For six adults (5 actual adults and a 12 year old -adults being everyone over 9 years old!) I paid:
Virgin Holidays 9 nights end of August but within UK school holidays: £5400 for flights, large people carrier car hire, all inclusive car insurance, 4 bed superior villa. (This went up by about 2.5k in various searches, I caught it at the right time.)
Tickets, 2-day Disney Park hoppers with additional 2 days water parks, 2-day Universal passes with free days, Kennedy Space Center with lunch with an astronaut, Clearwater Aquarium, Clearwater boat trip, Disney water park Polar Patio 6 person day hire: £3200 (could have been so much cheaper if they hadn't all wanted to do different things!)
Food and drink eating out for all meals: £2500
Airport taxi: £220
Total for 6 people: £11,400 and nobody warned me about the rain in August! The benefit of going at the end of the summer holidays is that we did not find the parks packed and there was no need to get anything like a Universal Express pass as we did not wait long for anything.
2 adults from the same party going back in September when the schools go back, 2 weeks, Disney hotel, 4 day Disney passes included: £2800 plus food, drink etc.
On this basis I reckon that all in you need £2000 for every person who is going.